The CD8+ cell phenotype mediating antiviral activity in feline immunodeficiency virus-infected cats is characterized by reduced surface expression of the CD8 beta chain.

The acute stage of feline immunodeficiency virus (FIV) infection is characterized by a CD8+ anti-FIV response that parallels the appearance of a CD8+ subpopulation with reduced expression of the beta chain (CD8 alpha + beta lo). The relationship between the CD8 alpha + beta lo phenotype and CD8+ anti-FIV activity was examined. Flow cytometric analysis of peripheral blood mononuclear cells with anti-CD8 beta chain monoclonal antibody 117 revealed that the CD8 alpha + beta lo phenotype expanded throughout the asymptomatic infection, constituting 80%-90% of the CD8 beta + cells in long-term-infected cats. Purified CD8 alpha + beta hi and CD8 alpha + beta lo subpopulations were analyzed for anti-FIV activity in an acute infection assay. Anti-FIV activity resided principally in the CD8 alpha + beta lo population and was demonstrated in acute FIV infections, as well as in long-term asymptomatic infections. These data suggest that a unique CD8 alpha + beta lo anti-FIV phenotype arises early in infection and may play a major role in eliminating virus and maintaining the asymptomatic infection.

Mucosally transmitted feline immunodeficiency virus induces a CD8+ antiviral response that correlates with reduction of cell-associated virus.

Intravaginal inoculation of cats with feline immunodeficiency virus (FIV) results in acute systemic infection accompanied by a strong CD8+ immune response that inhibits viral replication. CD8+ anti-FIV activity, revealed by increased FIV replication in peripheral blood mononuclear cells (PBMC) depleted of CD8+ lymphocytes, was detected by 6 weeks after inoculation and correlated with reduced PBMC-associated virus at 12, 16, and 32 weeks after inoculation. Some cats with strong CD8+ anti-FIV activity during acute infection did not seroconvert and yielded no evidence of FIV infection at later times. These data suggest that CD8+ immunity may play a major role in eliminating virus during primary transmucosal FIV infection and may down-regulate viral replication during asymptomatic infection.

Horizontal transmission of feline immunodeficiency virus with semen from seropositive cats.

The AIDS virus of cat species, feline immunodeficiency virus (FIV), has been used extensively as an animal model of HIV-1 infection. This felid lentivirus shares many molecular and biochemical traits with HIV-1 and causes similar immunologic and clinical perturbations, most notably CD4+ cell loss, impaired cell-mediated immunity and increased susceptibility to opportunistic pathogens. Previous reports have shown that FIV is transmitted horizontally by biting and vertically in utero and through nursing. Our objective was to determine whether FIV could be venereally transmitted in domestic cats. In the first experiment, susceptibility of the female reproductive tract to mucosal transmission of the FIV isolate, NCSU1, was demonstrated via intravaginal inoculation with infected cultured cells. We next identified virus in electroejaculates from asymptomatic, chronically FIV-NCSU1-infected, adult males. A fragment of FIV gag provirus DNA was detected by nested polymerase chain reaction (PCR) in nonfractionated seminal cells and in swim-up sperm preparations. Additionally, replication-competent virus was isolated from cell-free seminal plasma and seminal cells by co-cultivation with a feline CD4+ T-cell line. In the third study, queens were artificially inseminated via an intrauterine laparoscopic technique with electroejaculates from FIV-NCSU1-infected males. Of six inseminations carried out with fresh semen, three resulted in infection of queens. Lastly, immunohistochemical studies identified potential virus target cell populations in normal female reproductive tissues. In conclusion, these experiments indicate that FIV infection in domestic cats may provide a unique small animal model of sexual transmission of HIV-1.